JP7211215B2 - Color conversion information generation method, color conversion information generation program, and color conversion information generation device - Google Patents

Description

The present invention relates to a color conversion information generation method, a color conversion information generation program, and a color conversion information generation device.

2. Description of the Related Art Conventionally, there is known a technique of executing printing in consideration of printer characteristics. For example, Japanese Patent Application Laid-Open No. 2002-200003 describes a technique for executing printing that takes into consideration the characteristics of a printer by converting coordinate values in a space representing an arbitrary color into coordinate values in a space representing colors that can be output by a printer. It is In the following, for convenience of explanation, the space representing arbitrary colors will be referred to as "device-independent color space", and the colors defined as coordinate values in the device-independent color space will be referred to as "device-independent colors", which will be output by a printer. A space that represents possible colors is called a "device dependent color space", and a color defined as a coordinate value in the device dependent color space is called a "device dependent color". The information is called "conversion information".

JP 2006-157294 A

However, in the prior art, when printing device-independent colors with a printer, conversion information is required to accurately convert the device-independent colors from coordinate values in the device-independent color space to coordinate values in the device-dependent color space. Correction information to be corrected is generated, and the correction information is used to correct the coordinate values of the device dependent color space obtained from the conversion information based on the device independent color. For this reason, in the prior art, each time an output command for outputting a device-independent color is supplied to an output device, the correction information is used to obtain from the conversion information based on the coordinate values indicating the device-independent color. There is a problem that the process of correcting the coordinate values of the device-dependent color space is required, and the process of outputting the device-independent color takes time.

A color conversion information generation method according to a preferred aspect of the present invention accepts either or both of a first coordinate value in a first color space that defines a color and a name that indicates the color defined as the first coordinate value. converting the first coordinate values into second coordinate values of the second color space using a receiving step and first conversion information for converting the coordinate values of the first color space into coordinate values of the second color space; A first conversion step of converting and a first output device for outputting an image according to the coordinate values of the second color space measures the output image output according to the second coordinate values by a colorimetry device. , an obtaining step of obtaining the result of the colorimetry as a colorimetric coordinate value in the first color space; and a second transformation for converting the coordinate value in the second color space to the coordinate value in the first color space a second transformation step of transforming the second coordinate value into a third coordinate value in the first color space using information; a color difference between the first coordinate value and the colorimetric coordinate value; and the third coordinate value. a determination step of determining target coordinate values in the first color space based on the above; a searching step of searching for the fourth coordinate value satisfying a condition that the color difference between the coordinate value and the target coordinate value is smaller than the color difference between the third coordinate value and the target coordinate value; and a generating step of generating color conversion information for converting the first coordinate value or the name to the coordinate value of the second color space based on the fourth coordinate value.

A color conversion information generating program according to a preferred aspect of the present invention accepts either or both of a first coordinate value in a first color space that defines a color and a name that indicates the color defined as the first coordinate value. a receiving unit for converting the first coordinate values into second coordinate values in the second color space using first conversion information for converting the coordinate values in the first color space into coordinate values in the second color space; and a first output device for outputting an image according to the coordinate values of the second color space, the output image output according to the second coordinate values is measured by a colorimetry device, and an acquisition unit that acquires the result of colorimetry as colorimetric coordinate values in the first color space; a second conversion unit that converts the second coordinate value into a third coordinate value in the first color space, based on the color difference between the first coordinate value and the colorimetric coordinate value, and the third coordinate value , a determination unit for determining target coordinate values in the first color space, a fifth coordinate value in the first color space obtained by transforming the fourth coordinate value in the second color space using the second transformation information, and the target a searching unit for searching for the fourth coordinate value that satisfies a condition that the color difference between the coordinate value and the target coordinate value is smaller than the color difference between the third coordinate value and the target coordinate value; and the first coordinate value and the fourth coordinate value. The computer functions as a generator that generates color conversion information for converting the first coordinate value or the name into the coordinate value of the second color space based on and.

A color conversion information generating apparatus according to a preferred aspect of the present invention accepts either or both of a first coordinate value in a first color space that defines a color and a name that indicates the color defined as the first coordinate value. converting the first coordinate values into second coordinate values in the second color space using a receiving unit and first conversion information for converting the coordinate values in the first color space into coordinate values in the second color space; A first conversion unit that converts and a first output device that outputs an image according to the coordinate values of the second color space measures the output image output according to the second coordinate values by a colorimetric device. , an acquisition unit for acquiring the result of the colorimetry as a colorimetric coordinate value in the first color space; and a second transform for transforming the coordinate value in the second color space into the coordinate value in the first color space. a second conversion unit that converts the second coordinate value to a third coordinate value in the first color space using information; a color difference between the first coordinate value and the colorimetric coordinate value; and the third coordinate value. and a determination unit for determining target coordinate values in the first color space based on the above; a search unit for searching for the fourth coordinate value satisfying a condition that a color difference between the coordinate value and the target coordinate value is smaller than a color difference between the third coordinate value and the target coordinate value; a generation unit that generates color conversion information for converting the first coordinate value or the name to the coordinate value of the second color space based on the fourth coordinate value.

1 is a configuration diagram of a color conversion table generation system 1; FIG. The figure which shows the A2B table 1211. FIG. The figure which shows the B2A table 1212. FIG. The figure which shows the A2B table 1221. FIG. FIG. 4 is a diagram showing the cmyk color space CSD; The figure which shows the B2A table 1222. FIG. FIG. 4 is a diagram showing Lab color space CSI; FIG. 4 shows a color conversion table 126; 4 is a diagram showing an outline of generation of a color conversion table 126; FIG. 4 is a flowchart showing color conversion table generation processing; 4 is a flowchart showing color conversion table generation processing; FIG. 4 shows an example of a color conversion table generation screen 220; 4 is a flowchart showing search processing; The figure which shows initial value (DELTA)cmyk. 4 is a flowchart showing optimization problem solving processing. 4 is a flowchart showing registered cmyk value determination processing. 4 is a flowchart showing operations during print processing; FIG. 4 is a diagram showing a first color conversion flow; The figure which shows a 2nd color conversion flow. The figure which shows a 3rd color conversion flow. 1 is a block diagram of a color conversion table generation system 1a; FIG. FIG. 12 shows a DLP 127 for calibration; The figure which shows the outline|summary of generation|occurrence|production of DLP127 for a calibration. FIG. 12 shows a second printer property A2B table 1276; FIG. FIG. 12 shows a colorimetric result difference table 1274; FIG. 4 is a flowchart showing DLP generation processing for calibration; 4 is a flowchart showing DLP generation processing for calibration; 9 is a flowchart showing search processing in the second embodiment; 9 is a flowchart showing optimization problem solving processing in the second embodiment. The figure which shows the 1st color conversion flow in 2nd Embodiment. The figure which shows the 2nd color conversion flow in 2nd Embodiment. The figure which shows the 3rd color conversion flow in 2nd Embodiment. 11 is a flow chart showing operations during execution of print processing in the third modified example. The figure which shows the 1st color conversion flow in a 3rd modification.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, in each drawing, the dimensions and scale of each part are appropriately different from the actual ones. In addition, since the embodiments described below are preferred specific examples of the present invention, they are subject to various technically preferable limitations. It is not limited to these forms unless stated otherwise.

A. First Embodiment First, a color conversion table generation system 1 according to a first embodiment will be described.

A. 1. Overview of Color Conversion Table Generation System 1 FIG. 1 is a configuration diagram of the color conversion table generation system 1 . The color conversion table generation system 1 includes a host device 10 , a display device 20 , a colorimetry device 30 and a first printer 40 . The host device 10 is an example of a "color conversion information generating device". The first printer 40 is an example of a "first output device". The host device 10 can access the display device 20 , the colorimetry device 30 and the first printer 40 .

The host device 10 is a computer that controls the display device 20, the colorimetry device 30, and the first printer 40 to generate the color conversion table 126. FIG.

The display device 20 displays various images under the control of the host device 10 . For example, various display panels such as a liquid crystal display panel or an organic EL display panel are preferably used as the display device 20 . EL is an abbreviation for Electro Luminescence.

The first printer 40 is an inkjet printer that ejects ink to form an image on a medium according to instructions from the host device 10 . The medium is, for example, plain paper, a photograph, or recording paper such as a postcard. There are four ink colors: cyan, magenta, yellow, and black. Inks are not limited to these four colors. For example, the first printer 40 may use inks such as light cyan, light magenta, dark yellow, or light black. The first printer 40 of the first embodiment uses four colors of ink, cyan, magenta, yellow, and black.

The colorimetric device 30 measures the color of the image displayed on the medium by the first printer 40 and outputs a colorimetric value, which is the measured color value. The colorimetric device 30 outputs colorimetric values in the device independent color space. Note that the device independent color space is an example of the "first color space".
The device independent color space is, for example, the CIE L*a*b* color space or the CIE XYZ color space. CIE stands for Commission internationale de l'eclairage. In the following description, the device independent color space is assumed to be the CIE L*a*b* color space, and the CIE L*a*b* color space is simply referred to as the Lab color space CSI as shown in FIG. . Similarly, coordinate values in the Lab color space CSI are referred to as "Lab values".

The input device 16 is a device for a user to input information. The input device 16 is composed of one or more types of devices such as a pointing device, a keyboard, and a touch panel attached to the surface of the display device 20, for example.

The first communication IF 17 is a device that communicates with the colorimetric device communication IF 32 of the colorimetric device 30 . The second communication IF 18 is a device that communicates with the first printer communication IF 42 of the first printer 40 . The first communication IF 17, the second communication IF 18, the colorimetric device communication IF 32, and the first printer communication IF 42 are also referred to as network devices, network controllers, network cards, or communication modules, for example. The standards of the first communication IF 17, the second communication IF 18, the colorimetry device communication IF 32, and the first printer communication IF 42 can be USB, short-range wireless communication standards, or the like. USB is an abbreviation for Universal Serial Bus. The communication of the first communication IF 17, the second communication IF 18, the colorimetry device communication IF 32, and the first printer communication IF 42 may be wired, wireless, or network communication such as LAN or the Internet. LAN is an abbreviation for Local Area Network.

Host device 10 includes storage device 12 , control device 13 , input device 16 , first communication IF 17 and second communication IF 18 . IF is an abbreviation for Interface. The colorimetric device 30 includes a colorimetric device communication IF 32 . The first printer 40 includes a first printer communication IF42.

The storage device 12 is a recording medium readable by the control device 13, and stores a plurality of programs, various data used by the control device 13, an input profile 121, an output profile 122, a color library 124, a color conversion table 126, and , stores the LUT 128 without color correction. LUT is an abbreviation for Look Up Table. The storage device 12 is composed of one or more types of storage circuits such as ROM, EPROM, EEPROM, RAM, HDD, and SSD, for example. ROM is an abbreviation for Read Only Memory. EPROM stands for Erasable Programmable ROM. EEPROM is an abbreviation for Electrically Erasable Programmable ROM. RAM is an abbreviation for Random Access Memory. HDD is an abbreviation for Hard Dive Disk. SSD is an abbreviation for Solid State Drive.

An input profile 121 is a file that defines a color space. The output profile 122 is a file that indicates output characteristics of the first printer 40 . Color spaces include the above-described device independent color space and device dependent color space. Device dependent color spaces include the CMYK color space for representing colors that combine cyan, magenta, yellow, and black, the CMY color space for representing colors that combine cyan, magenta, and yellow, and red, green. , and an RGB color space that combines blue.
In the following description, simply referring to a profile is a generic term for the input profile 121 and the output profile 122 .

As described above, the device dependent color space includes the CMYK color space, CMY color space, RGB color space, and the like. For example, the input profile 121 may have color conversion tables for each of the CMYK color space, the CMY color space, and the RGB color space, and the output profile 122 may have color conversion tables for each of the CMYK color space, the CMY color space, and the RGB color space. You may have a table. However, for simplification of explanation, in the first embodiment, the input profile 121 and the output profile 122 are assumed to have only a color conversion table for the CMYK color space with respect to the device dependent color space.

The input profile 121 has an A2B table 1211 and a B2A table 1212 as color conversion tables. The output profile 122 has an A2B table 1221 and a B2A table 1222 as color conversion tables. Note that the input profile 121 may not have the A2B table 1211 and the B2A table 1212, but may have other tables used for color conversion. However, in the first embodiment, it is assumed that the input profile 121 has an A2B table 1211 and a B2A table 1212 . A2B table 1211, B2A table 1212, A2B table 1221, and B2A table 1222 will be described.

FIG. 2 is a diagram showing the A2B table 1211. As shown in FIG. In the following description, the color space in which the image information included in the print command generated by the user's operation represents a combination of cyan, magenta, yellow, and black will be indicated as "CMYK color space" in capital letters. . The A2B table 1221 is used to convert coordinate values in the CMYK color space to Lab values in the Lab color space CSI. Coordinate values in the CMYK color space are called "CMYK values". The A2B table 1211 indicates CMYK values and Lab values of N1 grid points in the CMYK color space. N1 is an integer of 1 or more.

A CMYK color space has C, M, Y, and K axes. The CMYK values are coordinate values indicating process colors. CMYK values have C, M, Y, and K values. The C value, M value, Y value, and K value are real numbers of 0 or more and 100 or less.
The Lab color space CSI has L, a, and b axes. Lab values have L, a, and b values.

There are two types of image information included in the print command: process color and spot color. A process color is a color expressed by a combination of four ink colors of cyan, magenta, yellow, and black. A spot color, on the other hand, is a premixed ink color. Spot colors are, for example, colors specified in a PANTONE (registered trademark) color sample book, colors specified in a DIC (registered trademark) color sample book, and the like.

FIG. 3 is a diagram showing the B2A table 1212. As shown in FIG. The B2A table 1212 is used to convert Lab values in the Lab color space CSI into coordinate values in the cmyk color space CSD shown in FIG. Coordinate values in the cmyk color space CSD are referred to as "cmyk values". In order to distinguish from the CMYK color space in the image information included in the print command, the color space representing the combination of cyan, magenta, yellow, and black input to the first printer 40 is referred to as the cmyk color space. Alphabetical. Furthermore, for ease of understanding, the space for representing colors dependent on the first printer 40 is expressed as cmyk color space CSD. The cmyk color space CSD is an example of the "second color space".

A cmyk value has a c value, a y value, an m value, and a k value. The c value, y value, m value, and k value are real numbers of 0 or more and 100 or less. The B2A table 1212 indicates cmyk values of N2 lattice points in the Lab color space CSI. N2 is an integer of 1 or more.

FIG. 4 is a diagram showing the A2B table 1221. As shown in FIG. The A2B table 1221 is used to convert cmyk values in the cmyk color space CSD to Lab values in the Lab color space CSI. Note that the A2B table 1221 is an example of "second conversion information".

The A2B table 1221 is a table storing Lab values reproducible over the entire cmyk value range of the first printer 40 dependent cmyk color space CSD.

FIG. 5 is a diagram showing the cmyk color space CSD. The cmyk color space CSD is a four-dimensional space with c, m, y, and k axes. For ease of illustration, FIG. 5 shows a three-dimensional space with c-, m-, and y-axes. The A2B table 1221 indicates Lab values at N3 grid points GDa in the cmyk color space CSD. N3 is an integer of 1 or more. White circles shown in FIG. 5 are grid points GDa. In FIG. 5, in order to suppress the complication of the drawing, only some of the plurality of grid points GDa are represented by reference numerals. The grid points GDa are arranged at equal intervals in the c-axis direction, m-axis direction, y-axis direction, and k-axis direction in the cmyk color space CSD. More specifically, the lattice points GDa are spaced apart in the c-axis direction by a distance Gc, in the m-axis direction by a distance Gm, in the y-axis direction by a distance Gy, and in the k-axis direction by a distance Gk (not shown).

FIG. 6 is a diagram showing the B2A table 1222. As shown in FIG. The B2A table 1222 is used to convert Lab values in the Lab color space CSI to cmyk values in the cmyk color space CSD. When the B2A table 1222 stores cmyk values reproducible by the first printer 40 for the entire Lab, the cmyk values are stored in consideration of gamut mapping for Lab values that cannot be reproducible by the first printer 40 . A gamut is a reproduction range of colors that can be expressed by a device. The B2A table 1222 is an example of "first conversion information".

FIG. 7 is a diagram showing the Lab color space CSI. Each record of the B2A table 1222 indicates cmyk values of N4 grid points GDb in the Lab color space CSI. N4 is an integer of 1 or more. White circles shown in FIG. 7 are grid points GDb. In FIG. 7, in order to suppress the complication of the drawing, only some of the plurality of grid points GDb are given reference numerals. The grid points GDb are arranged at regular intervals in the L-axis direction, the a-axis direction, and the b-axis direction in the Lab color space CSI. More specifically, the grid points GDb are spaced apart from each other in the L-axis direction by a distance GL, in the a-axis direction by a distance Ga, and in the b-axis direction by a distance Gb.

As shown in FIGS. 4 and 6, the output profile 122 has an A2B table 1221 used for color conversion from cmyk values to Lab values and a B2A table 1222 used for color conversion from Lab values to cmyk values. . The B2A table 1222 is a three-dimensional table with gamut mapping, and the A2B table 1221 is a four-dimensional table in which cmyk values representing colors that can be output are associated with Lab values. Therefore, when a certain Lab value is converted to a cmyk value by the B2A table 1222 and the cmyk value obtained by conversion is converted to a Lab value by the A2B table 1221, the obtained Lab value is the same value as the original Lab value. may not be Further, in the following description, a process of converting a certain Lab value into a cmyk value using the B2A table 1222 and converting the resulting cmyk value into a Lab value using the A2B table 1221 is referred to as "round-trip operation". Sometimes. By performing a round-trip operation, Lab values that simulate the printing of the first printer 40 can be obtained.

Returning to FIG. The color library 124 is used to convert spot color names to spot color Lab values. Hereinafter, the name of the spot color will be referred to as "spot color name" for simplification of explanation. A spot color name indicates a color represented by a Lab value. Spot color names are, for example, "Pantone P 41-8C" and "Pantone P 97-8C".
The color conversion table 126 is a table generated by this embodiment. The color conversion table 126 is used to convert the spot color Lab values SP_Lab into cmyk values. A cmyk value associated with the Lab value SP_Lab_ is referred to as a “registered cmyk value pcmyk”.

FIG. 8 is a diagram showing the color conversion table 126. As shown in FIG. As shown in FIG. 8, the color conversion table 126 has, for each spot color, the Lab value of the spot color and the registered cmyk value that reproduces the color closest to this Lab value. A Lab value SP_Lab ₁ and a Lab value SP_Lab ₂ are registered as Lab values of two spot colors in the color conversion table 126 shown in FIG. 8, and the registered cmyk value pcmyk ₁ is associated with the Lab value SP_Lab ₁ . _The registered cmyk value _pcmyk2 is associated with the Lab value SP_Lab2. In FIG. 8, each component of the Lab value SP_Lab ₁ is (SP_L ₁ , SP_a ₁ , SP_b ₁ ), each component of the Lab value SP_Lab ₂ is (SP_L ₂ , SP_a ₂ , SP_b ₂ ), and the registered cmyk value pcmyk Each component of ₁ is (pc ₁ , pm ₁ , py ₁ , pk ₁ ) and each component of registered cmyk value pcmyk ₂ is (pc ₂ , pm ₂ , py ₂ , pk ₂ ). Also, the color conversion table 126 may have spot color names instead of Lab values. Therefore, the color conversion table 126 can be used not only for spot color Lab values SP_Lab, but also for converting spot color names into cmyk values. However, in the first embodiment, the color conversion table 126 is described as having Lab values of spot colors and registered cmyk values that reproduce colors closest to the Lab values.

Returning to FIG. The no-color-correction LUT 128 is used to convert cmyk values into ink usage amounts INK shown in FIG. 9 by applying halftones. The amount of ink used INK is the amount of ink that can be optimally printed by the first printer 40 . In the first embodiment, the ink usage INK has four ink usages: c ink usage, m ink usage, y ink usage, and k ink usage.

The control device 13 is a processor that controls the entire host device 10 . The control device 13 performs various processes by reading programs from the storage device 12 and executing the read programs. The controller 13 is composed of one or more processors. Also, some or all of the functions of the control device 13 may be realized by hardware such as DSP, ASIC, PLD, or FPGA. DSP is an abbreviation for Digital Signal Processor. ASIC is an abbreviation for Application Specific Integrated Circuit. PLD is an abbreviation for Programmable Logic Device. FPGA is an abbreviation for Field Programmable Gate Array.

A. 2. Configuration of First Embodiment The control device 13 functions as a color conversion table generation unit 130 and a print processing unit 140 by reading and executing programs from the storage device 12 . The color conversion table generation unit 130 includes a reception unit 131, a first conversion unit 132, an acquisition unit 133, a second conversion unit 134, a first determination unit 135, a first search unit 136, and a first generation unit. 137. Print processing unit 140 includes a third conversion unit 142 and an output control unit 146 . The color conversion table generator 130 and the print processor 140 will be described with reference to FIG.

FIG. 9 is a diagram showing an outline of generation of the color conversion table 126. As shown in FIG. The accepting unit 131 accepts one or both of the spot color Lab value SP_Lab and the spot color name of the Lab color space CSI indicating the spot color by the user's operation of the input device 16 . Note that the spot color Lab value SP_Lab is an example of the "first coordinate value". A spot color is an example of "a color defined by the first coordinate value". When the receiving unit 131 receives only the spot color name, the control device 13 uses the color library 124 to identify the spot color Lab value SP_Lab corresponding to the received spot color name. For simplicity of explanation, it is assumed below that the reception unit 131 receives only the spot color Lab value SP_Lab in the first embodiment.

The first conversion unit 132 uses the B2A table 1222 to convert the spot color Lab value SP_Lab into device-dependent color coordinate values Initcmyk in the cmyk color space CSD. Note that the device-dependent color coordinate value Initcmyk is an example of the "second coordinate value".

Here, the conversion according to the profile is represented by the function ficc (first argument, second number, third argument). The first argument represents the profile to use. The second argument represents the color conversion table used in the profile represented by the first argument. More specifically, in the second argument, A2B indicates conversion from device dependent color to device independent color, and B2A indicates conversion from device independent color to device dependent color. The third argument represents coordinate values to be transformed.

As a specific processing content, ficc() will return the registered value if the value specified by the 3rd argument matches the value registered in the table specified by the 1st and 2nd arguments. Output the value associated with . On the other hand, if the value specified by the third argument does not match the values registered in the table specified by the first and second arguments, ficc() will Outputs the value obtained by interpolating from the value. The processing of the first conversion unit 132 can be rephrased by the following equation (1).
Initcmyk = ficc (output profile 122, B2A, SP_Lab) (1)

The acquisition unit 133 causes the colorimetry device 30 to measure the output image output by the first printer 40 in accordance with the device-dependent color coordinate value Initcmyk, and obtains the colorimetry result from the colorimetry device 30 in the Lab color space CSI. Get the color value cLab. The colorimetric value cLab is an example of a “colorimetric coordinate value”. More specifically, the controller 13 converts the device-dependent color coordinate value Initcmyk into the ink usage amount INK using the LUT 128 without color correction. The first printer 40 prints a spot color image based on the ink usage amount INK. The colorimetric device 30 measures the spot color image. The obtaining unit 133 obtains the colorimetric value cLab from the colorimetric device 30 .

The second conversion unit 134 converts the device-dependent color coordinate value Initcmyk into the device-independent color coordinate value InitLab of the Lab color space CSI. Note that the device-independent color coordinate value InitLab is an example of the "third coordinate value". The processing of the second conversion unit 134 can be rephrased by the following equation (2).
InitLab = ficc (output profile 122, A2B, Initcmyk) (2)
Note that it can be considered that the first conversion unit 132 and the second conversion unit 134 have performed a round-trip operation on the spot color Lab values to obtain the device-independent color coordinate values InitLab.

The first determination unit 135 determines a target Lab value TargetLab indicating a target color of the Lab color space CSI based on the device-independent color coordinate value InitLab and the difference value ΔLab between the spot color Lab value SP_Lab and the colorimetric value cLab. do. The target Lab value TargetLab is an example of the "target coordinate value". The difference value ΔLab may be a value obtained by subtracting each component of the colorimetric value cLab from each component of the spot color Lab value SP_Lab, or a value obtained by subtracting each component of the spot color Lab value SP_Lab from each component of the colorimetric value cLab. good. In the first embodiment, the difference value ΔLab is assumed to be a value obtained by subtracting each component of the colorimetric value cLab from each component of the spot color Lab value SP_Lab. For example, the first determination unit 135 determines the target Lab value TargetLab according to the following equation (3).
TargetLab = InitLab + ΔLab (3)
Note that if the difference value ΔLab is a value obtained by subtracting each component of the spot color Lab value SP_Lab from each component of the colorimetric value cLab, the first determination unit 135 calculates the difference value ΔLab from the device-independent color coordinate value InitLab. A value obtained by the subtraction is determined as the target Lab value TargetLab.

The first search unit 136 determines that the color difference between the provisional Lab value pLab _p of the Lab color space CSI obtained by converting the provisional cmyk value pcmyk _p of the cmyk color space CSD using the A2B table 1221 and the target Lab value TargetLab is the device-independent color A provisional cmyk value pcmyk _p that satisfies the condition that the color difference between the coordinate value InitLab and the target Lab value TargetLab is smaller is searched as the optimum cmyk value cmyk _st .
The color difference is, for example, a color difference ΔE ₀₀ represented by the CIE 2000 color difference formula, a color difference ΔE* ₉₄ represented by the CIE 1994 color difference formula, a color difference ΔE* _ab according to the Lab color system proposed in 1976, a so-called ΔE* ₇₆ , Alternatively, there is a color difference ΔE* _uv based on the CIE L*u*v* color system. In the first embodiment, ΔE ₀₀ is used as the color difference, and is hereinafter referred to as color difference ΔE ₀₀ .
The color difference ΔE ₀₀ can be obtained by a function f _ΔE00 (first argument, second argument). Details of the function f _ΔE00 ( ) are omitted for simplicity of explanation. The color difference ΔE ₀₀ between the provisional Lab value pLab _p and the target Lab value TargetLab is obtained by substituting the provisional Lab value pLab for the first argument and the target Lab value TargetLab for the second argument of the function f _ΔE00 ( ). . Similarly, the color difference ΔE ₀₀ between the device-independent color coordinate value InitLab and the target Lab value TargetLab is obtained by substituting the device-independent color coordinate value InitLab in the first argument of the function f _ΔE00 ( ) and the target Lab value in the second argument. Obtained by substituting TargetLab.
The optimum cmyk value cmyk _st is an example of the "fourth coordinate value". A Lab value obtained by converting the optimum cmyk value cmyk _st using the A2B table 1221 is an example of the “fifth coordinate value”.

The processing of the first search unit 136 has, for example, the following two modes. In the first mode, the first search unit 136 calculates the color difference ΔE ₀₀ between the provisional Lab value pLab _p and the target Lab value TargetLab. The temporary cmyk value pcmyk _{p that is the source of conversion of the temporary Lab value pLab p is} an arbitrary cmyk value. However, the provisional cmyk value pcmyk _p is preferably close to, and most preferably the same as, the device-dependent color coordinate value Initcmyk. If the condition that the color difference ΔE ₀₀ between the provisional Lab value pLab _p and the target Lab value TargetLab is smaller than the color difference ΔE ₀₀ between the device-independent color coordinate value InitLab and the target Lab value TargetLab, the first search unit 136 Output the provisional cmyk value pcmyk _p as the optimal cmyk value cmyk _st . On the other hand, if the color difference ΔE ₀₀ between the provisional Lab value pLab _p and the target Lab value TargetLab does not satisfy the condition described above, the first search unit 136 changes the provisional cmyk value pcmyk _p so that the optimum cmyk value cmyk _st is Repeat until found. The variation amount of the provisional cmyk value pcmyk _p is, for example, a fixed value.

In the second mode, the first search unit 136 converts the first provisional cmyk value pcmyk _p1 obtained by adding the first adjustment value Δcmyk1 to the provisional cmyk value pcmyk _p using the A2B table 1221, and converts the first provisional Lab value pLab _p1 into the target A first search process is executed to change the first adjustment value Δcmyk1 so that the output value of the objective function including the color difference ΔE ₀₀ from the Lab value TargetLab becomes smaller. Further, the first search unit 136 converts the second provisional cmyk value pcmyk _p2 obtained by adding the second adjustment value Δcmyk2 to the provisional cmyk value pcmyk _p by using the A2B table 1221 to obtain the second provisional Lab value pLab _p2 and the target Lab value TargetLab. A second search process is executed to change the second adjustment value Δcmyk2 so that the output value of the second objective function including the color difference ΔE ₀₀ of . Then, if the output value of the objective function at the end of the first search process is smaller than the output value of the objective function at the end of the second search process, the first search unit 136 determines Identify the first interim cmyk value pcmyk _p1 as the optimum cmyk value cmyk _st . On the other hand, if it is smaller than the output value of the second objective function at the end of the second search process, the first search unit 136 replaces the second provisional cmyk value pcmyk _p2 at the end of the second search process with the optimal cmyk value cmyk _st Identify as
The first provisional cmyk value pcmyk _p1 is an example of the "first provisional coordinate value". The first adjustment value Δcmyk1 is an example of the "first adjustment coordinate value". The first provisional Lab value pLab _p1 is an example of the "first transformed coordinate value". The second provisional cmyk value pcmyk _p2 is an example of the "second provisional coordinate value". The second adjustment value Δcmyk2 is an example of the "second adjustment coordinate value". The second provisional Lab value pLab _p2 is an example of the "second transformed coordinate value". The first adjustment value Δcmyk1 and the second adjustment value Δcmyk2 are four-dimensional vectors having Δc, Δm, Δy, and Δk as components.
Also, the first search unit 136 uses a plurality of provisional cmyk values pcmyk _p including the first provisional cmyk value pcmyk _p1 and the second provisional cmyk value pcmykp2 to determine the relationship between each provisional cmyk value pcmyk _p and the target Lab value TargetLab. A search process for changing the adjustment value Δcmyk may be performed by solving an optimization problem that minimizes the output value of the objective function including the color difference ΔE ₀₀ . In the first embodiment, the first search unit 136 executes search processing for each of the provisional cmyk values _pcmykp from the first provisional cmyk value pcmykp ₁ to the twenty-seventh provisional cmyk value pcmykp ₂₇ . Then, the first search unit 136 specifies the provisional cmyk value pcmyk _{p at the end of the search processing with the smallest output value of the objective function among the search processing for each provisional cmyk value pcmyk p as} the optimum cmyk value cmyk _st . .

The objective function is, for example, represented by the following formula (4).
f(Δcmyk)= _ΔE002 ⁺ w×V2 ⁺ C (4)
The w×V2 is a term provided to prevent the absolute value of any one of the components of the adjustment value ^Δcmyk from becoming excessively large. The factor w is a positive number. The coefficient w is preferably greater than 1 and 10 or less. The magnitude V is the magnitude of the adjustment value Δcmyk. The cost C is a constant that adjusts the provisional cmyk value pcmyk _p to satisfy the condition that each component of the cmyk value ranges from 0 to 100.

For solving the optimization problem, for example, the quasi-Newton method, Newton method, conjugate gradient method, or the like can be used. When using the quasi-Newton method, for example, the BFGS method or the DFP method can be used. BFGS is an abbreviation for the Broyden-Fletcher-Goldfarb-Shanno method. DFP stands for Davidon-Fletcher-Powell. As a method for solving the optimization problem, the BFGS method in the quasi-Newton method is used in the first embodiment.

As a method of identifying the provisional cmyk value pcmyk _p that satisfies the above conditions by solving the above-described optimization problem for each of the 27 initial values, the first search unit 136, for example, uses the 27 initial values Among the solution candidates obtained by solving the optimization problem for each of , the cmyk value indicated by the solution candidate with the smaller value of the objective function f(Δcmyk) is specified as the optimum cmyk value cmyk _st .

FIG. 9 shows that the first search unit 136 solves the optimization problem from the first provisional cmyk value pcmyk _p1 to the twenty-seventh provisional cmyk value pcmyk _p27 as initial values. The first provisional cmyk value pcmyk _p1 can be expressed as a value obtained by adding an initial value Δcmyk ₁ to the device-dependent color coordinate value Initcmyk. The provisional cmyk value pcmyk _{p1_1} shown in FIG. 9 is a value slightly changed from the first provisional cmyk value pcmyk _p1 . The twenty-seventh provisional cmyk value pcmyk _p27 can be expressed as a value obtained by adding the initial value Δcmyk ₂₇ to the device-dependent color coordinate value Initcmyk. The provisional cmyk value pcmyk _{p27_1} shown in FIG. 9 is a value slightly changed from the twenty-seventh provisional cmyk value pcmyk _p27 . The first provisional Lab value _{pLab p1} , provisional Lab value pLab _{p1_1} , twenty-seventh provisional Lab value pLab _p27 , and provisional Lab value pLab _{p27_1} shown in _FIG . 27 provisional cmyk value pcmyk _p27 and provisional cmyk value pcmyk _{p27_1} are converted using the A2B table 1221 .
Then, as shown in FIG. 9, the first search unit 136 solves the optimization problem using the first provisional cmyk values _{pcmyk p1} , _. , obtain the optimal solution candidate Δcmyk _pb27 . Next, the first search unit 136 identifies the optimum solution Δpcmyk _b that minimizes the objective function f(Δcmyk _pbn ) from the optimum solution candidates _{Δcmyk pb1} , . is specified as the optimal _cmyk value cmyk _st . n is a value from 1 to 27;

The first generator 137 generates the color conversion table 126 based on the spot color Lab value SP_Lab and the optimum cmyk value cmyk _st . As examples of generating the color conversion table 126, there are, for example, the following two modes. In the first mode, the first generation unit 137 associates the spot color Lab value SP_Lab with the optimum cmyk value cmyk _st itself and stores them in the color conversion table 126 . In the second mode, the first generation unit 137 duplicates the B2A table 1222, determines the adjustment amount of the output value for the nearest neighbor grid point of the spot color Lab value SP_Lab based on the optimum cmyk value cmyk _st , and duplicates it. The adjustment amount is reflected in the B2A table. Then, the first generator 137 converts the spot color Lab values SP_Lab into registered cmyk values pcmyk using the duplicated B2A table, associates the spot color Lab values SP_Lab with the registered cmyk values pcmyk, and converts them into the color conversion table 126. store in The duplicated B2A table is discarded. Therefore, the adjustment result is not reflected in the B2A table 1222. In the following description, the first generator 137 generates the color conversion table 126 according to the second aspect.

The image information included in the print command supplied to the first printer 40 during execution of the print process is either CMYK values, coordinate values in the RGB color space, Lab values indicating spot colors, or spot color names. . Coordinate values in the RGB color space are hereinafter referred to as "RGB values". When the image information is Lab values or spot color names, the print command supplied to the first printer 40 can be said to be a print command for printing device-independent colors. Note that the print command is an example of the "output command". In the first embodiment, for simplification of explanation, it is assumed that the image information included in the print command is a Lab value indicating a CMYK value spot color or a spot color name. A case where the image information included in the print command is CMYK values will be described with reference to FIG. 9, and a case where the image information included in the print command will be Lab values or spot color names will be described with reference to FIG.

When the image information indicating the image to be printed to be output to the first printer 40 is the CMYK values CMYK _in , the control device 13 converts the CMYK values CMYK _in into Lab values using the A2B table 1211, and further converts the Lab values into Lab values. Convert the value to a registered cmyk value pcmyk using the B2A table 1222 . The control device 13 converts the registered cmyk value pcmyk into the amount of ink used INK using the LUT 128 without color correction, and causes the first printer 40 to print an image showing the image information according to the amount of ink used INK.

Returning to FIG. When the image information indicating the image to be printed output to the first printer 40 is Lab values, the third conversion unit 142 uses the color conversion table 126 to convert the Lab values into cmyk values. If the image information indicating the image to be printed that is output to the first printer 40 is a spot color name, the third conversion unit 142 converts the spot color name to a Lab value using the color library 124, and further converts the color A conversion table 126 is used to convert Lab values to cmyk values.

The output control unit 146 causes the first printer 40 to output an image according to the cmyk values converted by the third conversion unit 142 . More specifically, the control device 13 converts the cmyk value into the ink usage amount INK using the LUT 128 without color correction, and prints an image according to the ink usage amount INK.

A. 3. Operation of Color Conversion Table Generation System 1 During Execution of Color Conversion Table Generation Processing FIGS. 10 and 11 are flowcharts showing the color conversion table generation processing. In step S<b>1 , the display device 20 displays a color conversion table generation screen 220 shown in FIG. 12 under the control of the control device 13 .

FIG. 12 is a diagram showing an example of the color conversion table generation screen 220. As shown in FIG. A color conversion table generation screen 220 is a screen used to generate the color conversion table 126 . The color conversion table generation screen 220 has an add button 221 , a delete button 222 , a print button 223 , a colorimetric button 224 , a spot color Lab value display area 226 , a colorimetric value display area 228 and a generate button 229 . The spot color Lab value display area 226 and the colorimetric value display area 228 have a record indicating information about the spot color for each spot color.

Each of the plurality of spot colors can be registered in the color conversion table 126 on the color conversion table generation screen 220 . However, for the sake of simplification of explanation, the following explanation assumes that one spot color is registered in the color conversion table 126 unless otherwise specified.

Returning the description to FIG. In step S<b>2 , the control device 13 accepts an operation on the color conversion table generation screen 220 . In step S<b>3 , the control device 13 determines whether or not an operation to press the add button 221 has been accepted. If the determination result in step S3 is affirmative, the control device 13 adds a new spot color record to the spot color Lab value display area 226 and the colorimetric value display area 228 in step S4. Update the generation screen 220 . The display device 20 displays the updated color conversion table generation screen 220. FIG. After displaying the updated color conversion table generation screen 220, the control device 13 returns to the process of step S2.

If the determination result in step S3 is negative, the control device 13 determines in step S5 whether or not an operation to press the delete button 222 has been received. If the determination result in step S5 is affirmative, in step S6, the control device 13 displays the color conversion table generation screen so as to delete the records in the spot color Lab value display area 226 and the colorimetric value display area 228. 220 is updated. The display device 20 displays the updated color conversion table generation screen 220. FIG. After displaying the updated color conversion table generation screen 220, the control device 13 executes the process of step S2 again.

If the determination result in step S5 is negative, the control device 13 determines in step S7 whether or not the pressing operation of the spot color Lab value display area 226 has been received. If the determination result in step S7 is affirmative, the control device 13 receives the spot color Lab value SP_Lab by the user's operation of the input device 16 in step S8. The color conversion table generation screen 220 shown in FIG. 12 shows an example in which an L value of 75.20, an a value of 15.40, and a b value of -2.60 are accepted.
There are the following two modes for user input. In the first mode, the user inputs the Lab value of the spot color, and the control device 13 displays the input Lab value in the spot color Lab value display area 226 . In the second aspect, the user inputs the color name of the spot color, the control device 13 uses the color library 124 to obtain the Lab value corresponding to the input color name, and the obtained Lab value is displayed in the spot color Lab value display area 226 .
After displaying the Lab value in the spot color Lab value display area 226, the control device 13 executes the process of step S2 again.

If the determination result in step S7 is negative, the control device 13 determines whether or not the press operation of the print button 223 has been accepted in step S9. If the determination result in step S9 is affirmative, the control device 13 uses the B2A table 1222 to convert the spot color Lab values SP_Lab into device-dependent color coordinate values Initcmyk in step S10. The process of step S10 can be rephrased by the above equation (1).

Next, in step S11, the controller 13 uses the no-color-correction LUT 128 to convert the device-dependent color coordinate value Initcmyk into the ink usage amount INK. Then, in step S12, the control device 13 causes the first printer 40 to print a spot color image based on the ink usage amount INK. After completing the process of step S12, the control device 13 executes the process of step S2 again.

If the determination result in step S9 is negative, the control device 13 determines whether or not the pressing operation of the colorimetric button 224 has been accepted in step S13. If the determination result in step S13 is affirmative, in step S14, the colorimetry device 30 measures the output image printed by the first printer 40, and the control device 13 acquires the colorimetry value cLab. The control device 13 displays the acquired colorimetric value cLab in the colorimetric value display area 228 . The color conversion table generation screen 220 shown in FIG. 1 shows an example in which an L value of 74.10, an a value of 13.90, and a b value of −1.20 are obtained as the colorimetric values cLab. After completing the process of step S14, the control device 13 executes the process of step S2 again.

If the determination result in step S13 is negative, the control device 13 determines in step S15 whether or not an operation to press the generate button 229 has been received. If the determination result in step S15 is negative, the control device 13 executes the process of step S2 again.

If the determination result in step S15 is affirmative, the control device 13 calculates a difference value ΔLab by subtracting the colorimetric value cLab from the spot color Lab value SP_Lab in step S21. The processing of step S21 can be rephrased by the following expression.
ΔLab = SP_Lab - cLab
Also, in step S22, the control device 13 uses the A2B table 1221 to convert the device-dependent color coordinate value Initcmyk into the device-independent color coordinate value InitLab. The processing of step S22 can be rephrased by the above equation (2).

Next, in step S23, the control device 13 calculates the target Lab value TargetLab by adding the difference value ΔLab to the device-dependent color coordinate value Initcmyk. The processing of step S23 can be rephrased by the above equation (3).

Then, the control device 13 executes search processing in step S24. Search processing will be described with reference to FIG. 13 .

FIG. 13 is a flowchart showing search processing. In the search process, the provisional Lab value pLab _p obtained by converting the provisional cmyk value pcmyk _p obtained by adding the adjustment value Δcmyk to the device-independent color coordinate value Initcmyk using the A2B table 1221 is the optimum solution Δcmyk _b to explore. More specifically, the search process sets an objective function f (Δcmyk) with an adjustment value Δcmyk as an argument, solves an optimization problem that minimizes the objective function f (Δcmyk), and finds the optimal solution Δcmyk _b Explore.

Since the quasi-Newton method performs a search using a differential function, it may converge to a local solution and a correct optimal solution may not be obtained. In order to suppress convergence to a local solution, the search process gives a plurality of initial values Δcmyk and applies the quasi-Newton method to each initial value Δcmyk to find the optimum solution candidate Δcmyk _pb . The search process then determines the optimum solution Δcmyk _b from the optimum solution candidates Δcmyk _pb for each initial value.

In the search process, the control device 13 substitutes 1 for the variable i in step S31. A variable i is a variable that identifies each of the plurality of initial values Δcmyk. In the following description, the initial value Δcmyk is a generic term for all initial values Δcmyk _i . Next, in step S32, the control device 13 sets an initial value Δcmyk _i of the adjustment value Δcmyk.

FIG. 14 is a diagram showing the initial value Δcmyk. Each grid point in the cmyk color space CSD shown in FIG. 14 indicates the position of the initial value Δcmyk. FIG. 14 shows the relationship between the initial value Δcmyk and only some grid points in order to keep the drawing from becoming complicated. In the following description, each component of the initial value Δcmyk _i is indicated as (Δci, Δmi, Δyi, Δki). In the search process, the initial value Δcmyk ₁ is (0, 0, 0, 0). In the first embodiment, centering on the initial value Δcmyk ₁ , the c value is shifted by a predetermined interval Sc at three points, the m value is shifted by a predetermined interval Sm at three points, and the y value is shifted by a predetermined interval Sy at three points. 27 initial values Δcmyk are prepared by The predetermined interval Sc, the predetermined interval Sm, and the predetermined interval Sy are real numbers greater than zero. Variable i is an integer of 1 or more and 27 or less. Δki is set to 0 in order to speed up the search process. Therefore, each component (Δci, Δmi, Δyi, Δki) of the initial value Δcmyk _i is as follows.

(Δc1, Δm1, Δy1, Δk1) = (0, 0, 0, 0)
(Δc2, Δm2, Δy2, Δk2) = (+Sc, 0, 0, 0)
(Δc3, Δm3, Δy3, Δk3) = (+Sc, 0, +Sy, 0)
…
(Δc12, Δm12, Δy12, Δk12) = (+Sc, +Sm, +Sy, 0)
…
(Δc25, Δm25, Δy25, Δk25) = (-Sc, -Sm, -Sy, 0)
…
(Δc27, Δm27, Δy27, Δk27) = (+Sc, -Sm, -Sy, 0)
As described above, Δki is set to 0 in the first embodiment, but it is also possible to shift Δcmyk ₁ by a predetermined interval Sk. The predetermined interval Sk is a real number greater than zero. In addition, although the number of initial values Δcmyk is 27 in the first embodiment, the number may be other than 27, such as 8 or 81.

The predetermined interval Sc, the predetermined interval Sm, and the predetermined interval Sy are, for example, 0.5 to 2 times the interval Gc, interval Gm, and interval Gy of the lattice points GDa indicated by the A2B table 1221 in the cmyk color space CSD. be able to. Expressed as a formula, it is as follows.
0.5×Gc≦Sc≦2×Gc
0.5×Gm≦Sm≦2×Gm
0.5×Gy≦Sy≦2×Gy
If the predetermined interval Sc, the predetermined interval Sm, and the predetermined interval Sy are set to 0.5 to 2 times the interval Gc, the interval Gm, and the interval Gy, the optimal solution Δcmyk _b can be searched efficiently.
When shifting by a predetermined interval Sk around Δcmyk ₁ , for example, it can be set to 0.5 times or more and 2 times or less the interval of the lattice points GDa in the k-axis direction.

Return the description to FIG. In step S33, the control device 13 substitutes the initial value Δcmyk _i for the adjustment value Δcmyk. The processing of step S33 can be rephrased by the following expression.
Δcmyk = Δcmyk _i

Next, in step S34, the control device 13 executes optimization problem solving processing. The optimization problem solving process when the variable i is 1 corresponds to the "first search process". Further, the optimization problem solving process when the variable i is 2 corresponds to the "second search process". The optimization problem solving process will be described with reference to FIG. 15 .

FIG. 15 is a flowchart showing optimization problem solving processing. The optimization problem solving process uses the BFGS method in the quasi-Newton method to find the optimum solution candidate Δcmyk _pb for one initial value Δcmyk _i out of a plurality of initial values Δcmyk _i .

In step S41, the control device 13 calculates the provisional cmyk value _pcmykp by adding the adjustment value Δcmyk to the device-dependent color coordinate value Initcmyk. The processing of step S41 can be rephrased by the following expression.
_pcmykp = Initcmyk + Δcmyk

Then, in step S42, the control device 13 uses the A2B table 1221 to convert the provisional cmyk value pcmyk _p to the provisional Lab value pLab _p . The processing of step S42 can be rephrased by the following expression.
pLab _p =ficc(output profile 122, A2B, pcmyk _p )

The processing from step S43 to step S45 is processing for obtaining each term of the objective function f(Δcmyk). The objective function f(Δcmyk) is given by the above equation (4).

In step S43, the control device 13 calculates the square of the color difference _ΔE00 between the provisional Lab value pLab _p and the target Lab value TargetLab. A formula for calculating the color difference ΔE ₀₀ is omitted for simplicity of explanation.

Further, in step S44, the control device 13 calculates the square of the magnitude V of the vector when the adjustment value Δcmyk is represented by the vector of the cmyk color space CSD.

Further, the control device 13 calculates the cost C in step S45. Since the provisional cmyk value pcmyk _p satisfies the condition that each component of the cmyk value can take a range of 0 to 100, the control device 13 calculates the cost C according to the following formula. In the following equation, each component of the temporary cmyk value pcmyk _p is (c _pp ,m _pp ,y _pp ,k _pp ).
If c _pp < 0, then C = -c _pp ×C _co
If c _pp >100, then C=(c _pp −100)×C _co
If m _pp < 0, then C = -m _pp ×C _co
If m _pp >100, then C = (m _pp -100) x C _co
If y _pp < 0, then C = -y _pp ×C _co
If y _pp >100, then C=(y _pp −100)×C _co
If k _pp < 0, then C = -k _pp ×C _co
If k _pp >100, then C = (k _pp -100) x C _co
Otherwise, C=0
The coefficient C _co is a positive number, preferably about 10 ³ or more and 10 ⁹ or less, which is sufficiently large compared to the range of 0 or more and 100 or less that each component of the cmyk value can take.

The control device 13 may calculate the cost C based on factors other than the condition that each component of the cmyk value can take a range of 0 to 100. For example, the control device 13 may add a value of 10 ³ or more and 10 ⁹ or less to the cost C when an error occurs when the processing of steps S41 to S45 is executed.

Since each term of the objective function f(Δcmyk) is obtained by the processing from step S43 to step S45, the control device 13 calculates the objective function f(Δcmyk) and obtains an output value in step S46.

In step S47, the control device 13 repeats the processing from step S41 to step S46 until the optimum solution candidate Δcmyk _pb that minimizes the output value of the objective function f(Δcmyk) is found. When the process of step S47 is performed first, it cannot be determined whether or not the output value of the objective function f(Δcmyk) is the minimum value. is slightly changed, and the process returns to step S41. This minute amount is determined based on the BFGS method. When the process of step S47 is performed for the second time or later, the control device 13 executes the process of step S48 if the optimum solution candidate Δcmyk _pb is not found. When the optimum solution candidate Δcmyk _pb is found, the control device 13 ends the series of processes shown in FIG. 15 and executes the process of step S35 shown in FIG.

Return the description to FIG. In step S35, the control device 13 determines whether or not the optimization problem solving process has been executed for all the initial values Δcmyk. If the determination result in step S35 is negative, that is, if there is an initial value Δcmyk for which the optimization problem-solving process has not yet been performed, the control device 13 increments the variable i by 1 in step S36 to start the process. Return to step S32. On the other hand, if the determination result in step S35 is affirmative, the control device 13 determines the optimum solution Δcmyk _b from the optimum solution candidates Δcmyk _pb for each initial value Δcmyk in step S37.

Then, in step S38, the control device 13 calculates the optimum cmyk value cmyk _st by adding the optimum solution Δcmyk _b to the device-dependent color coordinate value Initcmyk. The process of step S38 can be rephrased by the following expression.
_cmykst = Initcmyk + _Δcmykb
After completing the process of step S38, the control device 13 ends the series of processes shown in FIG. 13, and executes the process of step S25 shown in FIG.

Returning the description to FIG. In step S25, the control device 13 executes registration cmyk value determination processing, and ends the series of processing shown in FIGS. The registered cmyk value determination process will be described with reference to FIG.

FIG. 16 is a flowchart showing registration cmyk value determination processing. The control device 13 duplicates the B2A table 1222 of the output profile 122 in step S51. For example, assume that the storage device 12 is a HDD and RAM, and the B2A table 1222 is stored in the HDD. The control device 13 duplicates the B2A table 1222 stored in the HDD onto the RAM.

Next, in step S52, the control device 13 determines the adjustment amount of the output value for the adjacent lattice point of the spot color Lab value SP_Lab in the duplicated B2A table 1222 based on the optimum solution Δcmyk _b . The grid points to be adjusted are not only the closest grid points of the spot color Lab value SP_Lab, but also eight neighboring grid points located at each vertex of the cube containing the spot color Lab value SP_Lab. For example, the control device 13 determines the optimum solution Δcmyk _b itself as the adjustment amount.
Also, when registering a plurality of spot colors in the color conversion table 126, there is a possibility that some of the eight adjacent lattice points for the plurality of spot colors will be the same. The amount of adjustment when some of the eight neighboring grid points are the same will be described. In the duplicated B2A table, the control device 13 sets the adjustment amounts of the eight neighboring grid points GP _{SP_Lab1} including the spot color Lab value SP_Lab1 to the adjustment amounts based on the optimum solution Δcmyk _{b (SP_Lab1)} corresponding to the spot color Lab value SP_Lab1. Decide on Xn. Similarly, the control device 13 determines the adjustment amount Ym based on the optimum solution Δcmyk _{b (SP_Lab2)} corresponding to the spot color Lab value SP_Lab2 as the adjustment amount for the eight neighboring grid points GP _{SP_Lab2} including the spot color Lab value SP_Lab2. do. If there is a neighboring grid point included in both the 8 neighboring grid points GP _{SP_Lab1} and the 8 neighboring grid points GP _{SP_Lab2} , the control device 13 uses the average value of the adjustment amount Xn and the adjustment amount Ym to Update the adjustment amount of neighboring grid points included in .

Then, in step S53, the control device 13 reflects the adjustment amount in the duplicated B2A table.

Next, in step S54, the control device 13 converts the spot color Lab value SP_Lab into the registered cmyk value pcmyk using the duplicated B2A table. The processing of step S54 can be rephrased by the following expression.
pcmyk = ficc (duplicated B2A table, B2A, SP_Lab)

In step S55, the control device 13 calculates the difference d between the registered cmyk value pcmyk and the optimal cmyk value cmyk _st . Then, in step S56, the control device 13 determines whether or not a condition for ending the repeated processing is satisfied. There are two modes of termination conditions as follows. A first aspect of the termination condition is that the color difference ΔE00 between the Lab value obtained by converting the registered cmyk value pcmyk using the A2B table 1221 and the spot color Lab value _{SP_Lab} is equal to or less than a predetermined threshold. A second aspect of the termination condition is that the number of determinations made in step S56 reaches a predetermined number. When the determination result of step S56 is negative, the control device 13 returns to the process of step S52.

If the determination result in step S56 is affirmative, the control device 13 stores the spot color Lab value SP_Lab and the registered cmyk value pcmyk in the color conversion table 126 in step S57. Next, the control device 13 discards the duplicated B2A table in step S58. After completing the process of step S58, the control device 13 ends the series of processes shown in FIG.

When registering a plurality of spot colors in the color conversion table 126, the control device 13 may perform the processing from step S21 to step S25 shown in FIG. 11 for each spot color.

A. 4. Operation of Color Conversion Table Generation System 1 During Execution of Print Processing FIG. 17 is a flowchart showing the operation during execution of print processing. When receiving a print command supplied to the first printer 40 by a user's operation or the like, the control device 13 determines in step S61 whether or not the image information included in the print command is a spot color name. If the image information is a spot color name, it means that the spot color has been specified. If the determination result in step S61 is affirmative, the control device 13 uses the color library 124 to convert the spot color name into a Lab value in step S62. Then, in step S63, the control device 13 determines whether or not the image information is Lab values. If the determination result in step S61 is negative, that is, if the image information included in the print command is Lab values or CMYK values, the control device 13 also determines in step S63 whether or not the image information is Lab values. do.
If the determination result of step S63 is affirmative, the control device 13 determines whether or not the storage device 12 has the color conversion table 126 in step S64. If the determination result in step S64 is affirmative, the control device 13 prints the image indicated by the image information according to the first color conversion flow in step S65.

FIG. 18 is a diagram showing the first color conversion flow. In the first color conversion flow, the control device 13 uses the color conversion table 126 to convert Lab values Lab _in , which are image information, into registered cmyk values pcmyk. Next, the control device 13 converts the converted registered cmyk value pcmyk into the ink usage amount INK using the LUT 128 without color correction. Then, the control device 13 causes the first printer 40 to print the image indicated by the Lab value Lab _in on the medium p based on the converted ink usage amount INK.

Returning the description to FIG. If the determination result in step S64 is negative, the control device 13 prints the image indicated by the image information according to the second color conversion flow in step S66.

FIG. 19 is a diagram showing the second color conversion flow. In the second color conversion flow, the control device 13 converts Lab values Lab _in , which are image information, into cmyk values pcmyk using the B2A table 1222 . Next, the control device 13 converts the converted cmyk value pcmyk into the ink usage amount INK using the LUT 128 without color correction. Then, the control device 13 causes the first printer 40 to print the image indicated by the Lab value Lab _in on the medium p based on the converted ink usage amount INK.

Returning the description to FIG. If the determination result in step S63 is negative, in other words, if the image information is CMYK values, the control device 13 prints the image indicated by the image information according to the third color conversion flow in step S67.

FIG. 20 is a diagram showing the third color conversion flow. In the third color conversion flow, the control device 13 uses the A2B table 1211 to convert the CMYK values CMYK _in , which are image information, into Lab values. Next, the control device 13 converts the converted Lab values into cmyk values pcmyk using the B2A table 1222 . Next, the control device 13 converts the converted cmyk value pcmyk into the ink usage amount INK using the LUT 128 without color correction. Then, the control device 13 causes the first printer 40 to print the image indicated by the CMYK values CMYK _in on the medium p based on the converted ink usage amount INK.

After completing the process of step S65, step S66, or step S67, the control device 13 ends the series of processes shown in FIG.

A. 5. Effects of the First Embodiment As described above, in the color conversion table generation system 1, the control device 13 included in the host device 10 includes the reception unit 131, the first conversion unit 132, the acquisition unit 133, the first It functions as a second conversion unit 134 , a first determination unit 135 , a first search unit 136 and a first generation unit 137 . The reception unit 131 functions as a reception process. The first conversion unit 132 functions as a first conversion step. Acquisition unit 133 functions as an acquisition process. The second conversion section 134 functions as a second conversion step. The first decision unit 135 functions as a decision process. The first search unit 136 functions as a search process. The first generation unit 137 functions as a generation process.
The first generator 137 generates the color conversion table 126 used to convert Lab values corresponding to spot colors to cmyk values. As a result, when the first printer 40 prints the Lab values corresponding to the spot colors during the printing process, the cmyk values obtained from the B2A table 1222 are used using the correction information indicating the correction values corresponding to the spot colors. No correction process is performed to correct the Therefore, in the first embodiment, it is possible to reduce the time required for print processing compared to the case where this correction processing occurs when a print command for device-independent colors is supplied to the first printer 40. .
Further, when the contents of the B2A table 1222 are changed, if the correction information indicating the correction value corresponding to the spot color is used, it is necessary to change the contents of the correction information. the burden on is increased. On the other hand, in the first embodiment, even if the contents of the B2A table 1222 are changed, the color conversion table 126 does not need to be changed, and the burden of changing the contents of the B2A table 1222 can be suppressed. .

The first search unit 136 prepares a plurality of temporary cmyk values pcmyk _p and solves the optimization problem for each to specify the optimum cmyk value cmyk _st . In general, if an optimization problem is solved using an initial value, it may converge to a local solution and the correct optimum solution may not be obtained. In the first embodiment, by solving the optimization problem for each of a plurality of initial values, even if the solution obtained by solving the optimization problem for a certain initial value is a local solution, other If the solution obtained by solving the optimization problem for the initial value of is the optimum solution, the correct optimum solution can be obtained. Therefore, in the first embodiment, it is possible to improve the possibility of obtaining a correct optimal solution as compared with the case of solving the optimization problem using one initial value.

In the first embodiment, when image information included in a print command supplied to the first printer 40 is a Lab value corresponding to a spot color during execution of print processing, the third conversion unit 142 converts the color conversion table 126 is used to convert the Lab values into cmyk values, and the output control unit 146 causes the first printer 40 to output an image according to the cmyk values converted by the third conversion unit 142 . The third converting section 142 functions as a third converting step. The output control section 146 functions as an output control process. As a result, in the first embodiment, correction processing for correcting the cmyk value obtained from the B2A table 1222 using the correction information indicating the correction value corresponding to the spot color does not occur. Compared to , the time required for print processing can be shortened.

B. Second Embodiment A color conversion table generation system 1 according to the first embodiment includes a first printer 40 . On the other hand, the color conversion table generation system 1a in the second embodiment has a first printer 40 and a second printer 50 as two printers. In the second embodiment, a method will be described in which the color conversion table 126 generated using the first printer 40 is also used when the second printer 50 prints.
A color conversion table generation system 1a according to the second embodiment will be described below. In the second embodiment exemplified below, the elements whose actions and functions are the same as those of the first embodiment are denoted by reference numerals in the above description, and detailed descriptions thereof are appropriately omitted.

B. 1. Overview of Color Conversion Table Generation System 1a FIG. 21 is a configuration diagram of the color conversion table generation system 1a. The color conversion table generation system 1a includes a host device 10a, a display device 20, a colorimetry device 30, a first printer 40, and a second printer 50. The second printer 50 is an example of a "second output device." The host device 10 a can access the display device 20 , the colorimetry device 30 , the first printer 40 and the second printer 50 .

The second printer 50 is an inkjet printer having the same functions as the first printer 40 . However, printers have individual output characteristics, and the output characteristics vary. Due to this variation, when the first printer 40 and the second printer 50 print images represented by the same cmyk value, the colors of the printed images may differ from each other.

The host device 10 includes a storage device 12a, a control device 13a, an input device 16, a first communication IF17, a second communication IF18, and a third communication IF19. The third communication IF 19 is a device that communicates with the second printer communication IF 52 of the second printer 50 . The standards of the third communication IF 19 and the second printer communication IF 52 can be USB, short-range wireless communication standards, or the like. The communication of the third communication IF 19 and the second printer communication IF 52 may be wired, wireless, or network communication such as LAN or Internet.

Storage device 12a stores a plurality of programs, various data used by control device 13a, input profile 121, output profile 122, color library 124, color conversion table 126, DLP 127 for calibration, and LUT 128 without color correction. do. DLP is an abbreviation for Device Link Profile. The DLP 127 for calibration is an example of "color conversion information for calibration".

FIG. 22 is a diagram showing the DLP 127 for calibration. The DLP 127 for calibration indicates the correspondence relationship between the cmyk value cmyk0 and the correction value that brings the color of the image printed by the second printer 50 closer to the color of the image printed by the first printer 40 according to this cmyk value cmyk0. The correction value has, for example, the following two aspects.
The correction value in the first mode is the cmyk value cmyk1 that enables the second printer 50 to print an image showing colors that are close to the colors of the image printed by the first printer 40 described above. The correction value in the second mode is the difference between the cmyk value cmyk1 and the cmyk value cmyk0. In the following description, the correction value is assumed to be in the first mode, the cmyk value cmyk0 is referred to as "input cmyk value cmyk0", and the cmyk value cmyk1 is referred to as "corrected cmyk value cmyk1".

The calibration DLP 127 shown in FIG. 22 indicates corrected cmyk values cmyk1 at N5 grid points in the cmyk color space CSD. N5 is an integer of 1 or more.

B. 2. Configuration of Second Embodiment Returning to FIG. The control device 13a functions as a color conversion table generation unit 130, a print processing unit 140a, and a calibration DLP generation unit 150 by reading and executing programs from the storage device 12a. The print processing unit 140a includes a third conversion unit 142, a fourth conversion unit 144, and an output control unit 146a. The calibration DLP generation unit 150 includes a fifth conversion unit 151 , an identification unit 152 , a second determination unit 153 , a second search unit 154 and a second generation unit 155 . The calibration DLP generation unit 150 and the print processing unit 140a will be described with reference to FIG.

FIG. 23 is a diagram showing an overview of generation of the DLP 127 for calibration. The control device 13 a causes the first printer 40 to print a color chart CH _T , which is an image in which the color patches PA are arranged, according to the adjustment target cmyk value cmyk _S2 registered in the color conversion table 126 . The number of color patches PA matches the number of cmyk values cmyk _S2 to be adjusted. Similarly, the control device 13a causes the second printer 50 to print the color chart _CHP , which is an image in which the color patches PA are arranged, according to the adjustment target cmyk value cmyk _S2 . In this way, the control device 13a causes the first printer 40 and the second printer 50 to print the same adjustment target cmyk value cmyk _S2 . However, as described above, since the first printer 40 and the second printer 50 have different output characteristics, the color chart _CHT and the color chart _CHP produce different images.
The fifth conversion unit 151 uses the second printer characteristic A2B table 1276 to convert the adjustment target cmyk value cmyk _S2 to the adjustment target Lab value Lab _S2 of the Lab color space CSI.

FIG. 24 is a diagram showing an example of the second printer property A2B table 1276. As shown in FIG. The second printer characteristic A2B table 1276 includes cmyk values ccmyk corresponding to the color patches of the ECI chart in the cmyk color space CSD and colorimetric values in the Lab color space CSI obtained by colorimetrically measuring the ECI chart output by the second printer 50. The correspondence relationship with the colorimetric value cLab _{ECI_P} representing the result is shown. ECI is an abbreviation for European Color Initiative. A second printer characteristic A2B table 1276 shows Lab values at N6 grid points in the cmyk color space CSD. N6 is an integer of 1 or more. N6 is the number of color patches on the ECI chart. The lattice points of the second printer characteristic A2B table 1276 are normally arranged in the cmyk color space CSD so as to be substantially evenly spaced in the c-axis direction, m-axis direction, y-axis direction, and k-axis direction.

Return the description to FIG. The specifying unit 152 uses the colorimetric result difference table 1274 to specify the colorimetric value difference ΔLab _{T−P_S2} corresponding to the adjustment target Lab value Lab _S2 .

FIG. 25 is a diagram showing an example of the colorimetry result difference table 1274. As shown in FIG. The colorimetric result difference table 1274 indicates the correspondence relationship between the colorimetric value cLab _P and the colorimetric value difference ΔcLab _TP . The colorimetric value _{cLab P} indicates the result of colorimetry of the color chart CHP printed by the second printer 50 . The colorimetric value difference ΔcLab _TP is a value obtained by subtracting the colorimetric value cLab _P from the colorimetric value cLab _T. The colorimetric value cLab _T indicates the result of colorimetric measurement of the color chart CH _T printed by the first printer 40 . The colorimetric difference ΔcLab _TP has ΔL, Δa, and Δb. N7 records are registered in the colorimetry result difference table 1274 as the number of color patches PA. For example, in the j-th record, L _j , a _j , and b _j are registered as colorimetric values cLab _P corresponding to the j-th color patch PA. (ΔL _TP ) _j , (Δa _TP ) _j and (Δb _TP ) _j are registered as value differences ΔcLab _TP . j is an integer of 1 or more and N7 or less.

Since the same Lab value as the adjustment target Lab value Lab _S2 is registered in the colorimetric result difference table 1274, the specifying unit 152 determines the colorimetric value difference ΔcLab _TP corresponding to the registered Lab value as the colorimetric value Identify as the difference ΔcLab _{T-P_S2} .

Return the description to FIG. The second determination unit 153 determines the target Lab value TargetLab of the Lab color space CSI based on the adjustment target Lab value Lab _S2 and the colorimetric value difference ΔLab _{T−P_S2} . For example, the second determination unit 153 determines a value obtained by adding the colorimetric value difference ΔLab _{T−P_S2} to the adjustment target Lab value Lab _S2 as the target Lab value TargetLab of the Lab color space CSI.
Note that the colorimetric value difference may be a value obtained by subtracting the colorimetric value cLab _T from the colorimetric value cLab _P. In this case, the second determination unit 153 uses the value obtained by subtracting the colorimetric value difference corresponding to the adjustment target Lab value Lab _S2 from the adjustment target Lab value Lab _S2 as the target Lab value TargetLab of the Lab color space CSI. decide.

The second search unit 154 calculates the color difference ΔE ₀₀ between the provisional Lab value pLab _p of the Lab color space CSI obtained by converting the provisional cmyk value pcmyk _p of the cmyk color space CSD using the second printer characteristic A2B table 1276 and the target Lab value TargetLab. is smaller than the color difference _ΔE00 between the target Lab value Lab _S2 and the target _Lab value _TargetLab .
A specific search method for the optimum cmyk value cmyk _st can be the same method as the search method for the optimum cmyk value cmyk _st in the first embodiment.

FIG. 23 shows that the second search unit 154 solves the optimization problem using the first provisional cmyk value pcmyk _p1 to the twenty-seventh provisional cmyk value pcmyk _p27 as initial values. The first provisional cmyk value pcmyk _p1 can be expressed as a value obtained by adding the initial value Δcmyk ₁ to the target cmyk value cmyk _S2 . Similarly, the twenty-seventh provisional cmyk value pcmyk _p27 can be expressed as a value obtained by adding the initial value Δcmyk ₂₇ to the target cmyk value cmyk _S2 .
The first provisional Lab value _{pLab p1} and the twenty-seventh provisional Lab value _{pLab p27} shown in FIG. This is the value obtained by conversion.
Then, as shown in FIG. 23, the second searching unit 154 solves the optimization problem using the first provisional cmyk values _{pcmyk p1} , _. , obtain the optimal solution candidate Δcmyk _pb27 . Next, the second searching unit 154 identifies the optimum solution Δpcmyk _b that minimizes the objective function f( _{Δcmyk pbn} ) from the optimum solution candidates _{Δcmyk pb1} , . is specified as the optimum _cmyk value cmyk _st . n is a value from 1 to 27;

The second generator 155 generates the calibration DLP 127 based on the adjustment target cmyk value cmyk _S2 and the optimum cmyk value cmyk _st . For example, the second generation unit 155 stores the adjustment target cmyk value cmyk _S2 in the calibration DLP 127 in association with the optimum cmyk value cmyk _st . Furthermore, if only the adjustment target cmyk value cmyk _S2 is adjusted, gradation collapse occurs around the adjustment target _{cmyk value cmyk S2 .} Adjust the correction cmyk value cmyk1 relative to the value cmyk0.

Returning the description to FIG. When the image information indicating the image to be printed output to the second printer 50 is Lab values or spot color names, the fourth conversion unit 144 uses the DLP 127 for calibration to convert the Convert the cmyk value to a corrected cmyk value cmyk1. The output control unit 146 causes the second printer 50 to print an image according to the corrected cmyk value cmyk1 converted by the fourth conversion unit 144 .
In the second embodiment, when causing the first printer 40 to output an image, the control device 13a does not use the DLP 127 for calibration and converts the The first printer 40 is caused to output an image according to the obtained cmyk value.

B. 3. Operation of Color Conversion Table Generation System 1 During Execution of Calibration DLP Generation Processing FIGS. 26 and 27 are flowcharts showing the calibration DLP generation processing. In step S101, the control device 13a generates the calibration DLP 127 in which the input cmyk value cmyk0 and the corrected cmyk value cmyk1 are the same. Next, in step S102, the control device 13a causes the first printer 40 to print a color chart CH _T including each color patch PA according to the adjustment target cmyk value cmyk _S2 registered in the color conversion table 126. FIG. In step S103, the colorimetric device 30 measures the color chart CH _T printed by the first printer 40, and the control device 13a acquires the colorimetric value cLab _T of each color patch PA from the colorimetric device 30. do.

Further, in step S104, the control device 13a causes the second printer 50 to print a color chart _CHP including each color patch PA according to the adjustment target cmyk value cmyk _S2 registered in the color conversion table 126. FIG. Then, in step S105, the colorimetric device 30 measures the color chart CHP, and the control device _13a acquires the colorimetric value _cLabP of each color patch PA.

Next, in step S106, the control device 13a determines the cmyk value ccmyk corresponding to the color patch of the ECI chart and the colorimetric value cLab _{ECI_P} of each color patch printed by the second printer 50 according to the cmyk value ccmyk. to generate a second printer property A2B table 1276. As a specific generation method, the control device 13 a substitutes the cmyk value ccmyk into the cmyk value of the second printer characteristic A2B table 1276 . Further, the control device 13a associates the colorimetric value cLab _{ECI_P} , which indicates the colorimetric result of the ECI chart printed by the second printer 50 with the cmyk value ccmyk, with the substituted cmyk value ccmyk. Specifically, the control device 13a substitutes the aforementioned colorimetric value cLab _{ECI_P} into the Lab value of the same record as the substituted cmyk value ccmyk in the second printer characteristic A2B table 1276 .

Then, in step S107, the control device 13a generates a colorimetric result difference table 1274 based on the adjustment target cmyk value cmyk _S2 , the colorimetric value cLab _T , and the colorimetric value cLab _P. As a specific generation method, the control device 13a converts the colorimetric value _{cLab P indicating} the colorimetric result of the color chart CHP printed by the first printer 40 with a certain adjustment target cmyk value to Lab in the colorimetric result difference table 1274. Assign to value. Furthermore, the control device 13a subtracts the substituted colorimetric value cLab _P from the colorimetric value cLab _T indicating the colorimetric result of the color chart CH _T printed by the first printer 40 with a certain cmyk value, thereby Calculate the value difference ΔcLab _TP . Then, the control device 13a associates the aforementioned colorimetric value difference ΔcLab _TP with the substituted Lab value. Specifically, the control device 13a substitutes the aforementioned colorimetric value difference ΔcLab _TP into the ΔcLab value of the same record as the substituted Lab value in the colorimetric result difference table 1274 .

Next, in step S108, the control device 13a uses the second printer characteristic A2B table 1276 to convert the adjustment target cmyk value cmyk _S2 registered in the color conversion table 126 into the adjustment target Lab value Lab _S2 . The processing of step S108 can be rephrased by the following expression.
Lab _S2 = ficc (second printer characteristics A2B table 1276, A2B, cmyk _S2 )

Generation of the calibration DLP 127 is possible even if a plurality of spot colors are registered in the color conversion table 126 . However, for the sake of simplification of explanation, the following explanation will take as an example the case where one spot color is registered in the color conversion table 126 unless otherwise specified.

Then, in step S109, the control device 13a refers to the colorimetric result difference table 1274 to specify the colorimetric value difference ΔcLab _{T−P_S2} corresponding to the adjustment target Lab value Lab _S2 .

Next, in step S110, the control device 13a calculates the target Lab value TargetLab by adding the colorimetric value difference ΔcLab _{T−P_S2} to the adjustment target Lab value Lab _S2 . The processing of step S110 can be rephrased by the following expression.
TargetLab = Lab _S2 + ΔcLab _{T-P_S2}

Then, in step S111, the control device 13a executes the search process in the second embodiment. Search processing in the second embodiment will be described with reference to FIG. 28 .

FIG. 28 is a flowchart showing search processing in the second embodiment. The search processing in the second embodiment is substantially the same as the search processing in the first embodiment. Only differences from the search processing in the first embodiment will be described below.

In step S134, the control device 13a executes an optimization problem solving process. The optimization problem solving process will be described with reference to FIG. 29 .

FIG. 29 is a flowchart showing optimization problem solving processing in the second embodiment. The optimization problem-solving process in the second embodiment is substantially the same as the optimization problem-solving process in the first embodiment. Only differences from the optimization problem solving process in the first embodiment will be described below.

In step S141, the control device 13a calculates the provisional cmyk value _pcmykp by adding the adjustment value Δcmyk to the adjustment target cmyk value cmyk _S2 . The processing of step S141 can be rephrased by the following expression.
pcmyk _p = cmyk _S2 + Δcmyk

In step S142, the control device 13a uses the second printer property A2B table 1276 to convert the provisional cmyk value pcmyk _p to the provisional Lab value pLab _p . The processing of step S142 can be rephrased by the following expression.
pLab _p =ficc (second printer characteristics A2B table 1276, A2B, pcmyk _p )

If the determination result of step S147 is affirmative, the control device 13a terminates the series of processes shown in FIG. 29 and executes the process of step S135.

Return the description to FIG. In step S138, the control device 13a calculates the optimum cmyk value cmyk _st by adding the optimum solution Δcmyk _b to the adjustment target cmyk value cmyk _S2 . The processing of step S138 can be rephrased by the following expression.
cmyk _st = cmyk _S2 + Δcmyk _b
After completing the process of step S138, the control device 13a ends the series of processes shown in FIG. 28, and executes the process of step S121 shown in FIG.

Returning the description to FIG. In step S121, the control device 13a adjusts the corrected cmyk value cmyk1 of the calibration DLP 127 based on the optimum cmyk value cmyk _st . As specific adjustment methods, there are the following two aspects.

In the first mode, the controller 13a controls the input cmyk values cmyk0 of the DLP 127 for calibration, which are 16 neighboring lattice points, which are the vertices of the multi-dimensional hypercube containing the optimum cmyk value cmyk _st . The corrected cmyk value cmyk1 corresponding to the value cmyk0 is to be adjusted. For example, the control device 13a expresses each component of the _i -th corrected cmyk value cmyk1 among the 16 corrected cmyk values cmyk1 to be adjusted as c1i, _m1i , _y1i , and _k1i , Let the components of the cmyk value cmyk _st be denoted by cTarget, mTarget, yTarget, and kTarget. i is an integer from 1 to 16; The control device 13a adjusts the correction cmyk value cmyk1 of the calibration DLP 127 as follows.

_c1i = cTarget
_m1i = mTarget
_y1i = yTarget
k1 _i = kTarget

In the second mode, after the adjustment according to the first mode, the control device 13a performs a smoothing process so as to smooth the corrected cmyk values cmyk1 of the DLP 127 for calibration. The corrected cmyk value cmyk1 of the DLP 127 for calibration is adjusted again based on the obtained optimum solution. The smoothing process is, for example, an interpolation calculation process using a four-dimensional cubic spline function.

In step S122, the control device 13a executes black retention processing. The black holding process is a process for holding the amount of black to be used in order to suppress the graininess of ink dots. Specifically, the black retention process adjusts k1 of the corrected cmyk value cmyk1 to be larger than 0 when k0 of the input cmyk value cmyk0 of the calibration DLP 127 is larger than 0, and Adjust k1 to 0.

Next, in step S123, the control device 13a executes pure color retention processing. The pure color retention process is a process in which when the input cmyk value cmyk0 of the calibration DLP 127 is cyan, magenta, or yellow, the corrected cmyk value cmyk1 is also the same pure color as the input cmyk value cmyk0. A pure color refers to a color without ink contamination. As a specific example, if the input cmyk value cmyk0 _i indicates cyan, c0 _i of the input cmyk value cmyk0 _i is greater than zero and m0 _i , y0 _i , and k0 _i are zero. The pure color preservation process adjusts c1 _i of the corrected cmyk value cmyk1 _i to be greater than zero and m1 _i , y1 _i , and k0 _i to zero.

After completing the process of step S123, the control device 13a ends the series of processes shown in FIGS.

B. 4. Operation of Color Conversion Table Generation System 1 During Execution of Printing The only difference between the conversion flow and the third color conversion flow is that the calibration DLP 127 is used when the second printer 50 prints. Therefore, the description and illustration of the flowchart showing the operation during execution of the printing process in the second embodiment will be omitted, and the first color conversion flow and the second color conversion flow in the second embodiment when the second printer 50 prints , and the third color conversion flow will be described below.

FIG. 30 is a diagram showing the first color conversion flow in the second embodiment. In the first color conversion flow, the control device 13a uses the color conversion table 126 to convert Lab values Lab _in , which are image information, into registered cmyk values pcmyk. Next, the control device 13 a converts the converted registered cmyk value pcmyk into a corrected cmyk value pcmyk′ according to the output characteristics of the second printer 50 using the calibration DLP 127 . Then, the control device 13a converts the corrected cmyk value pcmyk' into the ink usage amount INK using the LUT 128 without color correction. Next, the control device 13a causes the second printer 50 to print the image indicated by the Lab value Lab _in on the medium p based on the converted ink usage amount INK.

FIG. 31 is a diagram showing the second color conversion flow in the second embodiment. In the second color conversion flow, the control device 13a uses the B2A table 1222 to convert Lab values Lab _in , which are image information, into cmyk values pcmyk. Next, the control device 13 a converts the converted cmyk value pcmyk into a corrected cmyk value pcmyk′ according to the output characteristics of the second printer 50 using the calibration DLP 127 . Then, the control device 13a converts the corrected cmyk value pcmyk' into the ink usage amount INK using the LUT 128 without color correction. Then, the control device 13a causes the second printer 50 to print the image indicated by the Lab value Lab _in on the medium p based on the converted ink usage amount INK.

FIG. 32 is a diagram showing the third color conversion flow in the second embodiment. In the third color conversion flow, the control device 13a uses the A2B table 1211 to convert the CMYK values _CMYKin , which are image information, into Lab values. Next, the control device 13a uses the B2A table 1222 to convert the converted Lab values into cmyk values pcmyk. Next, the control device 13 a converts the converted cmyk value pcmyk into a corrected cmyk value pcmyk′ according to the output characteristics of the second printer 50 using the calibration DLP 127 . Then, the control device 13a converts the corrected cmyk value pcmyk' into the ink usage amount INK using the LUT 128 without color correction. Then, the control device 13a causes the second printer 50 to print the image indicated by the CMYK values CMYK _in on the medium p based on the converted ink usage amount INK.

B. 5. Effects of the Second Embodiment As described above, when the image information included in the print command supplied to the second printer 50 is Lab values, the fourth conversion unit 144 uses the calibration DLP 127 to The cmyk value converted by the third conversion unit 142 is converted into the corrected cmyk value cmyk1, and the output control unit 146 outputs the image to the second printer 50 according to the corrected cmyk value cmyk1 converted by the fourth conversion unit 144. print. The fourth conversion section 144 functions as a fourth conversion step. It can be said that the color conversion table 126 is commonly used by the first printer 40 and the second printer 50 . Thus, even in a color conversion information generation system having multiple printers, there is no need to generate the color conversion table 126 for each printer. Furthermore, since the DLP 127 for calibration is used to cause the second printer 50 to print an image, an image corresponding to the output characteristics of the second printer 50 is printed. Therefore, even without the color conversion table 126 for the second printer 50, when the second printer 50 prints a spot color image, the color reproduction accuracy of the spot color can be improved.
Further, as shown in FIG. 22, the calibration DLP 127 is a multidimensional LUT, so compared to the case of using a one-dimensional LUT, the cmyk values converted by the third conversion unit 142 are c, Color reproduction accuracy can be further improved when all colors of m, y, and k are mixed colors.

Further, the control device 13 a functions as a fifth converting section 151 , a specifying section 152 , a second determining section 153 , a second searching section 154 and a second generating section 155 . The fifth conversion unit 151 functions as a fifth conversion step. The specifying unit 152 functions as a specifying step. The second determination unit 153 functions as a second determination step. The second search section 154 functions as a second search step. The second generation unit 155 functions as a second generation step. The second generation unit 155 creates a correspondence between the input cmyk value cmyk0 and the corrected cmyk value cmyk1 that brings the color of the image printed by the second printer 50 closer to the color of the image printed by the first printer 40 according to the input cmyk value cmyk0. Generate a calibration DLP 127 that indicates the relationship. By using the generated calibration DLP 127 when executing the printing process, when the second printer 50 prints a spot color image, the color reproduction accuracy of the spot color can be improved.

C. Modifications Each of the above forms can be modified in various ways. Specific modification modes are exemplified below. Two or more aspects arbitrarily selected from the following examples can be combined as appropriate within a mutually consistent range. It should be noted that, in the modifications illustrated below, the reference numerals referred to in the above description will be used for the elements that have the same actions and functions as those of the embodiment, and the detailed description of each will be omitted as appropriate.

C. 1. First Modification In the first and second embodiments, the input profile 121 and the output profile 122 are assumed to have only the color conversion table for the CMYK color space for the device dependent color space for the sake of simplification of explanation. , but not limited to this. For example, the input profile 121 may have an A2B table used for converting from RGB values to Lab values instead of or in addition to the A2B table 1211 . Similarly, output profile 122 may have a B2A table used to convert from Lab values to RGB values instead of B2A table 1222 . Furthermore, the output profile 122 may have an A2B table used for converting from RGB values to Lab values instead of or in addition to the A2B table 1221 . RGB values can take values between 0 and 255 inclusive.
On the premise that the input profile 121 has the A2B table 1211 and the A2B table used for converting from RGB values to Lab values, if the determination result in step S63 is negative, the control device 13 determines that the image information is CMYK values. or RGB values. When the image information is CMYK values, the control device 13 converts the CMYK values of the image information into Lab values using the A2B table 1211 . On the other hand, when the image information is RGB values, the control device 13 converts the RGB values of the image information into Lab values using the A2B table used for converting from RGB values to Lab values.
Also, if the output profile 122 has an A2B table and a B2A table for RGB values, the cost C in steps S45 and S145 is set to the condition that each component of the RGB values can take a range of 0 to 255, and the provisional RGB values are A constant that adjusts to satisfy The control device 13 calculates the cost C according to the following formula. In the following equations, each component of the provisional RGB values is (R _pp , G _pp , B _pp ).
If R _pp < 0, then C = -R _pp ×C _co
If R _pp >255, then C = (R _pp −255)×C _co
If G _pp < 0, then C = -G _pp ×C _co
If G _pp >255, then C = (G _pp −255)×C _co
If B _pp < 0, then C = -B _pp ×C _co
If B _pp >255, then C = (B _pp −255)×C _co
Otherwise, C=0
The coefficient C _co is a positive number, and is preferably about 10 ³ or more and 10 ⁹ or less, which is sufficiently large compared to the range of 0 or more and 100 or less that each component of the RGB values can take. Note that if the output profile 122 has an A2B table and a B2A table for RGB values instead of the A2B table 1221 and B2A table 1222, the RGB color space is an example of the "second color space."

C. 2. Second Modification In the second embodiment, when the image information included in the print command supplied to the second printer 50 is Lab values corresponding to spot colors, the third conversion unit 142 uses the color conversion table 126 to Then, the second printer 50 may output an image according to the cmyk values converted by the third conversion unit 142 . In other words, the control device 13a may cause the second printer 50 to output an image without using the DLP 127 for calibration. For example, if there is no significant difference in the output characteristics between the first printer 40 and the second printer 50, the second modified example may be adopted. As a result, if the output characteristics of the first printer 40 and the second printer 50 are not significantly different, when the second printer 50 prints a spot color image, the color reproduction accuracy of the spot color can be improved. can.

C. 3. Third Modification As described above, the color conversion table 126 may have spot color names instead of Lab values. Hereinafter, the third modified example will be described as a modified example from the first embodiment. For example, when a spot color name is accepted instead of the spot color Lab value SP_Lab in step S8, the controller 13 stores the accepted spot color name and registered cmyk value pcmyk in the color conversion table 126 in step S57. do.

FIG. 33 is a flow chart showing the operation when print processing is executed in the third modified example. When receiving a print command supplied to the first printer 40 by a user's operation or the like, the control device 13 determines in step S151 whether the image information included in the print command is a Lab value or a spot color name. If the determination result in step S151 is affirmative, the control device 13 determines whether or not the storage device 12 has the color conversion table 126 in step S152. If the determination result in step S152 is affirmative, the control device 13 prints the image indicated by the image information according to the first color conversion flow in step S153.

FIG. 34 is a diagram showing the first color conversion flow in the third modified example. In the first color conversion flow, when the image information is the Lab value Lab _in , the control device 13 uses the color conversion table 126 to convert the Lab value Lab _in to the registered cmyk value pcmyk. Alternatively, if the image information is the spot color name SName _in , the control device 13 uses the color conversion table 126 to convert the spot color name SName _in into the registered cmyk value pcmyk. Since the subsequent processing is the same as the first color conversion flow in the first embodiment, the explanation is omitted.

Returning the description to FIG. If the determination result in step S152 is negative, the control device 13 determines whether the image information is a spot color name in step S154. If the determination result in step S154 is affirmative, in step S155, the color library 124 is used to convert the spot color name into a Lab value. Then, in step S156, the control device 13 prints the image indicated by the image information according to the second color conversion flow. Further, when the determination result of step S154 is negative, that is, when the image information is Lab values, the control device 13 also executes the process of step S156. The second color conversion flow in the third modified example is the same as the second color conversion flow in the first embodiment, so the explanation is omitted.

If the determination result in step S151 is negative, in other words, if the image information is CMYK values, the control device 13 prints the image indicated by the image information according to the third color conversion flow in step S157. The third color conversion flow in the third modified example is the same as the third color conversion flow in the first embodiment, so description thereof will be omitted.
After completing the process of step S153, step S156, or step S157, the control device 13 ends the series of processes shown in FIG.

C. 4. OTHER MODIFICATIONS In each of the above embodiments, the spot color is an example of "the color defined as the first coordinate value", but the present invention is not limited to this. For example, the receiving unit 131 may receive some Lab values other than spot colors. More specifically, the receiving unit 131 may receive a cyan Lab value, a magenta Lab value, a yellow Lab value, or a black Lab value. Instead, a Lab value arbitrarily set by the user may be accepted.

In each of the above embodiments, the first printer 40 and the second printer 50 are ink jet printers, but the present invention is not limited to this. For example, an electrophotographic printer such as a laser printer that uses toner as a coloring material, a three-dimensional printer, a display device, or the like may be used. A display device is, for example, a display or a projector.

In each of the above embodiments, the objective function f(Δcmyk) has been described as represented by Equation (4), but is not limited to this. The objective function f(Δcmyk) may be, for example, a formula (4) with the cost C removed, or a formula with w×V ² removed. Furthermore, although ΔE ₀₀ ² is included in the formula (4), ΔE ₀₀ may be included instead of ΔE ₀₀ ² . Similarly, equation (4) includes w×V ² , but w×V may be included instead of w×V ² .

In each of the above embodiments, when executing the DLP 127 generation process for calibration, the control device 13a does not need to execute at least one of step S122 and step S123.

In each of the above embodiments, a color conversion information generation program configured to cause the above host device 10 to function as each part of the above host device 10, or a computer-readable record recording the color conversion information generation program It can also be considered as a medium. The recording medium is, for example, a non-transitory recording medium, and may include optical recording media such as CD-ROMs, as well as any known recording media such as semiconductor recording media and magnetic recording media. Further, in each of the above-described modes, it is also specified as a color conversion information generation method according to each of the above-described modes.

Reference Signs List 1, 1a Color conversion table generation system 10, 10a Host device 13, 13a Control device 14 Output control unit 16 Input device 20 Display device 30 Colorimetric device 40 First Printer 50 Second printer 121 Input profile 122 Output profile 126 Color conversion table 130 Color conversion table generation unit 131 Reception unit 132 First conversion unit 133 Acquisition unit 134 2nd conversion section 135 1st determination section 136 1st search section 137 1st generation section 140, 140a print processing section 142 3rd conversion section 144 4th conversion section 146 , 146a... output control unit, 150... DLP generation unit for calibration, 151... fifth conversion unit, 152... identification unit, 153... second determination unit, 154... second search unit, 155... second generation unit, 1221 ... A2B table, 1222 ... B2A table, 1274 ... colorimetry result difference table, 1276 ... second printer characteristic A2B table.

Claims (7)

a receiving step of receiving one or both of a first coordinate value of a first color space defining a color and a name indicating a color defined as the first coordinate value;
A first conversion method for converting the first coordinate values into second coordinate values in the second color space using first conversion information for converting the coordinate values in the first color space into coordinate values in the second color space; a conversion step;
A first output device that outputs an image according to the coordinate values of the second color space measures the output image according to the second coordinate values using a colorimetry device, and the result of the colorimetry is an obtaining step of obtaining as colorimetric coordinate values in the first color space;
converting the second coordinate values into third coordinate values of the first color space using second conversion information for converting the coordinate values of the second color space into the coordinate values of the first color space; 2 a conversion step;
a determination step of determining a target coordinate value in the first color space based on the difference between the first coordinate value and the colorimetric coordinate value and the third coordinate value;
A color difference between a fifth coordinate value in the first color space obtained by converting the fourth coordinate value in the second color space using the second conversion information and the target coordinate value is the third coordinate value and the target coordinate value. a searching step of searching for the fourth coordinate value that satisfies the condition that the color difference is smaller than the value;
color conversion information for converting one or both of the first coordinate value and the name to the coordinate value of the second color space based on the first coordinate value and the fourth coordinate value; a production process;
A computer-implemented method of generating color conversion information. The searching step includes
An objective function including a color difference between a first transformation coordinate value obtained by transforming a first provisional coordinate value obtained by adding a first adjustment coordinate value to an arbitrary coordinate value in the second color space using the second transformation information and the target coordinate value. executing a first search process for changing the first adjustment coordinate value so that the output value of
An output value of an objective function including a color difference between a second transformed coordinate value obtained by transforming a second provisional coordinate value obtained by adding a second adjusted coordinate value to the arbitrary coordinate value using the second transformation information and the target coordinate value is small. Execute a second search process for changing the second adjustment coordinate value so that
When the output value of the objective function at the end of the first search process is smaller than the output value of the objective function at the end of the second search process, the first provisional value at the end of the first search process identifying a coordinate value as the fourth coordinate value;
When the output value of the objective function at the end of the second search process is smaller than the output value of the objective function at the end of the first search process, the second provisional value at the end of the second search process A step of specifying a coordinate value as the fourth coordinate value,
2. The method for generating color conversion information according to claim 1. The computer
When the image information included in the output command supplied to the first output device is the coordinate value or the name of the first color space, the color conversion information is used to convert the image information into the second color space. a third conversion step of converting to coordinate values;
an output control step of causing the first output device to output an image indicated by the image information according to the coordinate values of the second color space converted in the third conversion step;
3. The method for generating color conversion information according to claim 1, wherein: The output control step includes
When an output command is supplied to a second output device that outputs an image corresponding to the coordinate values of the second color space, the second color obtained by converting the image information included in the output command by the third conversion step. causing the second output device to output an image indicated by the image information according to the spatial coordinate values;
4. The method for generating color conversion information according to claim 3, comprising: Calibration indicating a correspondence relationship between the coordinate values of the second color space and correction values for bringing the colors of the image output by the second output device closer to the colors of the image output by the first output device according to the coordinate values. a fourth conversion step of converting the coordinate values of the second color space converted in the third conversion step into correction values using color conversion information for
The output control step includes:
causing the second output device to output an image indicated by the image information according to the correction value converted in the fourth conversion step;
5. The method of generating color conversion information according to claim 4. a receiving unit that receives one or both of a first coordinate value in a first color space that defines a color and a name that indicates the color defined as the first coordinate value;
A first conversion method for converting the first coordinate values into second coordinate values in the second color space using first conversion information for converting the coordinate values in the first color space into coordinate values in the second color space; converter,
A first output device that outputs an image according to the coordinate values of the second color space measures the output image according to the second coordinate values using a colorimetry device, and the result of the colorimetry is an acquisition unit that acquires colorimetric coordinate values in the first color space;
converting the second coordinate values into third coordinate values of the first color space using second conversion information for converting the coordinate values of the second color space into the coordinate values of the first color space; 2 conversion unit,
a determination unit that determines a target coordinate value in the first color space based on the difference between the first coordinate value and the colorimetric coordinate value and the third coordinate value;
A color difference between a fifth coordinate value in the first color space obtained by converting the fourth coordinate value in the second color space using the second conversion information and the target coordinate value is the third coordinate value and the target coordinate value. a search unit that searches for the fourth coordinate value that satisfies the condition that the color difference from the value is smaller than the value;
color conversion information for converting one or both of the first coordinate value and the name to the coordinate value of the second color space based on the first coordinate value and the fourth coordinate value; generator,
A program that generates color conversion information that makes a computer function as a computer. a reception unit that receives either or both of a first coordinate value in a first color space that defines a color and a name that indicates the color defined as the first coordinate value;
A first conversion method for converting the first coordinate values into second coordinate values in the second color space using first conversion information for converting the coordinate values in the first color space into coordinate values in the second color space; a conversion unit;
A first output device that outputs an image according to the coordinate values of the second color space measures the output image according to the second coordinate values using a colorimetry device, and the result of the colorimetry is an acquisition unit that acquires colorimetric coordinate values in the first color space;
converting the second coordinate values into third coordinate values of the first color space using second conversion information for converting the coordinate values of the second color space into the coordinate values of the first color space; 2 conversion unit;
a determination unit that determines target coordinate values in the first color space based on the difference between the first coordinate value and the colorimetric coordinate value and the third coordinate value;
A color difference between a fifth coordinate value in the first color space obtained by converting the fourth coordinate value in the second color space using the second conversion information and the target coordinate value is the third coordinate value and the target coordinate value. a searching unit that searches for the fourth coordinate value that satisfies the condition that the color difference from the value is smaller than the value;
color conversion information for converting one or both of the first coordinate value and the name to the coordinate value of the second color space based on the first coordinate value and the fourth coordinate value; a generator;
A color conversion information generating device comprising:

Images